I would be a bit surprised if the original 2x6 are 20' long. If
they met at some mid point and were side lapped, this would have
occurred over a wall, that wall was then a load bearing wall.
That load bearing wall would have another wall or girder below it,
also load bearing. I assume you do not have trusses if you were
able to deck out large expanses. I don't know that you gained
much trading out 3/4 T&G for 3/4 plywood, they would both be rated
about the same.

The length of the joists is measured from bearing to bearing. If
they truly span 20' they have no load bearing ability. #2 SYP
joists carrying a ceiling are maxed out at just over 15'.

here is an easy calculator that will let you play with the
numbers:
http://www.awc.org/calculators/span/...izontal+ Span

--
______________________________
Keep the whole world singing . . . .
DanG (remove the sevens)




"Mikepier" wrote in message
...
I am nearing completion of my attic project. I recently put in an
attic stairs and putting in 3/4" OSB plywood for the floor,
replacing
the old T&G planks I had up there. I live in a split level 50
year old
house. The attic is 2X6's spaced 16"OC. It spans approx 20'
X20'.
Below are some walls forming a bedroom closet .Although I am not
sure
if this is a load bearing wall for the attic, I would think it
does
add some support. But realistically how much weight can be put
up
there? Is there some sort of guidline?